Enterics

Question 1

What defines enterics?

Answer 1

1) rod-shaped
2) gram-negative
3) occuring in the GI tract
4) facultative anaerobes

Question 2

What are three main enteric bacteria?

Answer 2

1) Shigella
2) Salmonella
3) Escherichia

Question 3

Which sites do enteric bacteria infect?

Answer 3

Any site!

Question 4

What are some common community-acquired enteric infections?

Answer 4

enteritis or colitis. cystitis, pyelo

Question 5

What does nosocomial infection mean?

Answer 5

infection originating in the hospital

Question 6

What is a major nosocomial infection?

Answer 6

Opportunistic Klebsiella pneumoniae infection

Question 7

What is the average size of bacteria of Enterobacteriaceae?

Answer 7

0.5-2.0 microns

Question 8

How are Enterobacteriaceae microbes motile?

Answer 8

peritrichous flagella

Question 9

What are the two non-motile species of Enterobacteriaceae?

Answer 9

1) Klebsiella

2) Shigella

Question 10

What is the most common selective media for enterics?

Answer 10

MacConkey agar

Question 11

What is an important distinction for selective isolation of enterics?

Answer 11

Lactose fermentation

Question 12

How are Enterobacteriaceae species identified?

Answer 12

biochemical reactions

Question 13

How are subtypes of Enterobacteriaceae bacteria identified?

Answer 13

serotyping of antigens

Question 14

What are the three antigens of enterics?

Answer 14

O antigen
H antigen
K antigen

Question 15

What is the O antigen?

Answer 15

O polysaccharide of LPS

Question 16

What is the H antigen?

Answer 16

flagella

Question 17

What is the K antigen?

Answer 17

capsule

Question 18

What is the exception to K antigen?

Answer 18

Vi-antigen of Salmonella

Question 19

Where can you find E.coli?

Answer 19

As part of the normal commensal flora of the Gi tract

Question 20

How are E.coli turned into pathogens?

Answer 20

Through the uptake of pathoenicity-associated islands, phages, and plasmids

Question 21

How have pathovars of E.coli evolved?

Answer 21

through HGT!

Question 22

What is EHEC?

Answer 22

Enterohemorrhagic E.coli

Question 23

What is the most abundant facultative anaerobe in the gut?

Answer 23

E. coli

Question 24

What does EHEC produce?

Answer 24

hemorrhagic colitis

Question 25

Why is the primary infection of EHEC not of real concern?

Answer 25

it is usually self-resolving and not fatal

Question 26

What do 15% of EHEC infections evolve into?

Answer 26

hemolytic uremic syndrome

Question 27

What can hemolytic uremic syndrome lead to?

Answer 27

CNS manifestations and acute renal failure

Question 28

Where is the incidence of EHEC the greatest?

Answer 28

developed countries

Question 29

Is O157:H7 the only serotype which causes hemorrhagic colitis?

Answer 29

no!

Question 30

What is the primary reservoir of EHEC?

Answer 30

cattle

Question 31

Is EHEC pathogenic in cattle?

Answer 31

no

Question 32

How do you transmit EHEC?

Answer 32

fecal-oral route

Question 33

What is the infectious dose of EHEC and what is significant about this?

Answer 33

10-100 bacteria, which is very low

Question 34

Is stomach acid a strong barrier to intestinal infection?

Answer 34

Yes.

Question 35

Can a lack of stomach acid lead to a higher susceptibility to infection?

Answer 35

Yes.

Question 36

What is a pathogenic feature of EHEC?

Answer 36

A/E lesions

Question 37

What are A/E lesions?

Answer 37

Attaching and effacing lesions. These are parts of the intestinal epithelium which the bacteria uses to inject in proteins and take over the cells

Question 38

How does pathogenic E. coil promote diarrhea?

Answer 38

1) tight junction disruption | 2) loss of absorptive surface area

Question 39

What does Shiga toxin bind?

Answer 39

Gb3 receptors

Question 40

Why is Shiga toxin called Shiga-like toxin in E.coli?

Answer 40

It shares similarity to Shiga toxin produced in virulent strains of Shigella

Question 41

Which is the more potent of the Shiga-like toxins?

Answer 41

Stx-2

Question 42

What encodes for Stx in E.coli?

Answer 42

lambda phage

Question 43

Why is the treatment of EHEC with abx controversial?

Answer 43

Because it leads to larger release of Shiga toxin and thus worse symptoms.

Question 44

Why are there systemic sequela from EHEC?

Answer 44

Stx binds globotriaosylceramide receptors which are prominent in the endothelium of the various organs, especially the kidneys

Question 45

How does Shiga or Shiga-like toxin work?

Answer 45

deadenylates 60S rRNA subunit

Question 46

What are the classic triad of symptoms of dysentery?

Answer 46

1) abdominal cramping 2) tenesmus 3) frequent, small-volume, bloody, mucoid discharge

Question 47

What is tenesmus?

Answer 47

Urge to defecate without or without actual production of fecal matter

Question 48

How do the strains of Shigella line up in terms of pathogenicity?

Answer 48

sonnei < flexneri << dyseneteriae

Question 49

What is the fatality rate in S. dyseneteriae epidemics?

Answer 49

5-15%

Question 50

What is Shigella thought to be a pathovar of?

Answer 50

E.coli

Question 51

What is the significance of fecal leukocytes?

Answer 51

invasive enteric pathogens provoke an inflammatory response resulting in high fecal leukocyte count

Question 52

What are the predominant Shigella infections in the US?

Answer 52

S. sonnei

Question 53

What is the primary reservoir for Shigella?

Answer 53

humans

Question 54

What is the infectious dose for Shigella and is it high or low?

Answer 54

<200 bacteria, low!

Question 55

What is the US incidence of Shigella infections?

Answer 55

~15k/year

Question 56

What are the primary targets of Shigella infections?

Answer 56

1) travelers | 2) children in day care

Question 57

How many global infections of Shigella are there?

Answer 57

150 million per year

Question 58

Which is the most common strain of Shigella in the world?

Answer 58

Flexneri

Question 59

How does Shigella infect the intestines?

Answer 59

Phagocytosis by the M cell, and then makes its way to the basolateral membrane. It then replicates intracellularly and spreads through the actin cytoskeleton.

Question 60

Which strain has Shiga toxin?

Answer 60

Shigella dysenteriae Type 1

Question 61

What is the difference between EHEC and Shiga toxin in Shigella?

Answer 61

The gene for Shiga toxin in Shigella is in the bacterial genome rather than a phage

Question 62

What differentiates Salmonella from the other Enterobacteriaceae species?

Answer 62

1) produces H2S | 2) phase variably motile

Question 63

Which types of infections are worse: broad host-range or narrow host-range?

Answer 63

Narrow host-range

Question 64

What are the two clinical presentations of Salmonella infections?

Answer 64

1) gastroenteritis | 2) Typhoid fever